1. Field of the Invention
This invention relates to a model toy, and more particularly to a wheel assembly for a model airplane.
2. Description of the Related Art
Referring to FIGS. 1 and 2, a conventional wheel assembly for a model airplane includes a housing unit 1, a pneumatic cylinder 2 disposed pivotally on the housing unit 1, and a wheel unit 3 disposed pivotally on the housing 1 and driven by the pneumatic cylinder 2. The housing unit 1 includes a housing body 101 and two aligned lugs 102 formed integrally with the housing body 101. The housing body 101 has two aligned side plates 103, two aligned pivot holes 104 formed respectively through lower end portions of the side plates 103, and two aligned guide slots 405 formed respectively through the side plates 103 and located respectively above the pivot holes 104. Each of the guide slots 405 has a curved section 405′ and two positioning sections 405″ extending respectively and upwardly from two opposite ends of the curved section 405′. The pneumatic cylinder 2 has a cylinder body 201 disposed pivotally between the lugs 102, a piston rod 202 connected movably to the cylinder body 201, and a driving rod 203 connected fixedly to and perpendicular to an end of the piston rod 202. The driving rod 203 extends through the guide slots 405. The wheel unit 3 includes a stop block 301 disposed within the housing body 101, a swing rod 302 having one end connected fixedly to the stop block 301, and two wheels 303 disposed on the other end of the swing rod 302. The stop block 301 has an integral pivot pin 301′ extending through the pivot holes 104, and a retaining slot 301″. The driving rod 203 is received slidably within the retaining slot 301″.
The piston rod 202 is movable relative to the cylinder body 201 between an extended position shown in FIG. 1 and a retracted position shown in FIG. 2. When the piston rod 202 is disposed in the extended position, the wheel unit 3 is disposed in an upright landing position. When the piston rod 202 is disposed in the retracted position, the wheel unit 3 is disposed in a generally horizontal idle position.
The use of the pneumatic cylinder 2 raises an instability issue. Inparticular, since the piston rod 202 moves relative to the cylinder body 201 at a high speed, rebounding of the driving rod 203 occurs at the ends of each of the curved sections 405′ during movement of the driving rod 203 within the guide slots 405. Thus, it is difficult for the driving rod 203 to move fully into the positioning sections 405″. That is, the wheel unit 30 cannot be locked effectively at the idle position and the landing position.